Not Applicable
Not Applicable
Infrared motion sensors such as those used for detecting human targets are typically subjected to various sources of radiation during their operation. Furthermore, motion sensors using mirrored optics are generally unprotected from various undesired wavelengths of incoming radiation. As a result, most of the energy that reaches the mirror surface is reflected and focused onto the infrared detector. This causes false alarms and/or other inaccurate detection events.
Sunlight, as well as well as tungsten/halogen lamp sources such as automobile headlamps, produce one type of electromagnetic radiation that is known to promote false alarms in infrared motion sensors. These radiation sources emit radiation in both the visible (e.g., 360 nm to 760 nm) and the infrared (e.g., 760 nm to 50 xcexcm) spectrum. Accordingly, compliance testing of infrared motion sensors in various countries often involves the use of a halogen light source at fairly intense levels (e.g., 2000 to 6000 lux) to determine the immunity of the motion sensor to this type of radiation.
It has been the attempt of many manufacturers of motion sensors to develop improved ways to make the infrared sensing elements less susceptible to the effects of these types of light sources. For example, some sensors use a protective absorbing layer beneath the reflective layer of the mirror (see, for example, U.S. Pat. No. 5,608,220 to Wieser et al., incorporated herein by reference) to remove potentially harmful radiation from the detector path. However, there is still a need for a more effective manner in which to inhibit visible and near infrared light (sometimes referred to as xe2x80x9cwhite lightxe2x80x9d in the motion sensor industry) to protect the sensing element(s).
By way of example, and not of limitation the invention comprises a method of reducing the incidence of visible and near-infrared light impinging on a reflective surface of an optical reflector by overlaying said reflective surface with a layer of non-crystalline carbon material. The invention also comprises a mirror having a substrate base, a layer of reflective material adjacent to the substrate base, and a light absorbing layer adjacent to the layer of reflective material. In the preferred embodiment of the invention, a diamond-like-coating (DLC) protective layer is placed on top of a reflective (e.g., metallized) mirror surface. This amorphous diamond coating has been developed for this application by Diamonex Performance Products, Allentown, Pa. and is referred to by Diamonex as xe2x80x9cDLC-Bxe2x80x9d.
An object of the invention is to coat the surface of a mirror with a protective layer that absorbs broad-band visible and near-infrared radiation so that said radiation is reduced before it reaches the infrared (IR) sensor.
Another object of the invention is to coat the surface of a mirror with a material that acts as a protective over-coating to prevent damage to the mirror surface due to abrasions, oxidation, corrosion, or atmospheric contamination.
Another object of the invention is to coat the surface of a mirror with a material that can be xe2x80x9ctunedxe2x80x9d to selectively block a specific wavelength of IR and/or visible energy (to below 10% of incident radiation) which are determined to be most adverse to the performance of the infrared sensor.
Another object of the invention is to coat the surface of a mirror with a material that functions as an optical xe2x80x9cnotchxe2x80x9d filter, with excellent suppression of selectable wavelengths, while otherwise being a reasonably good reducer of broad-band visible and near-infrared (NIR) radiation.
In addition, the coating has been shown to have little impact in the mid-infrared portion of the spectrum, where typical infrared motion sensors operate. In contrast, other alternative solutions, such as silicon-based windows or filters, will still reduce the amount of available mid-infrared energy by more than 20%. The present invention, however, deters MIR radiation by 5% or less.
Applications of this technology include, but are not limited to, lighting controls, motion sensors for security and lighting and other controls, temperature sensors and thermal controls, and thermal imaging.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.